Process for improving the surface characteristics of cellulose hydrate films



United States Patent 4 Claims. of. ins-r93 The present invention relates to a process for improving the surface characteristics of cellulose hydrate films in which the films are passed through a bath which in addition to containing softening agents also contain additions of lubricants and/or anchoring agents and to which dispersions having a high content of oxide aerogels are added as antiblocking agents in order to provide such improved surface characteristics that they can be stacked or rolled up for storage before being subjected to other processing such as lacquering, coating, cutting, printing and the like without the danger of their sticking together.

In order to improve the physical properties of cellulose hydrate films, such as extension and elasticity, they are normally treated with solutions of softeners such as glycerine or diand triglycols. Depending upon the intended use of the films such films contain in general 12 to 20% softeners. As a result of the use of such softeners, depending upon the quantity contained in the softener baths, certain disadvantagous properties are engendered therein in that the stickiness of such films is greatly increased and such stickiness often can lead to difficulties in the subsequent processing of the softened films.' For example, the surfaces of rolled up film stick together (block) so that it cannot be removed from the roll without difficulty and often tears 0E. Such tendency of rupture of the film is especially disadvantageous and disturbing to production when the film is to be processed on automatic machines such as roller cutters, printing machines or bag making machines.

For further improvement of the film surface characteristics increasing use has been made in recent years of a number of certain organic compounds which, despite varying chemical composition, either are high molecular weight organic bases and/or electropositively charged colloids. Such products which are used as so-called anchoring agents in the processing of cellulose hydrate films in order to be able, for example, to apply a firmly adhering lacquer coating, for instance, are compounds of the polyethylene imine type, urea formaldehyde precondensates (partial condensation products), melamine formaldehyde precondensates and similar compounds. In addition to such anchoring agents use also is made of so-called lubricants which also almost without exception are organic bases or electropositively charged colloids.

In the production of cellophane these so-called anchoring agents and/or lubricants are added in certain quantities either to the bath containing softening agents or to a preceding bath. The anchoring agents and/ or lubricants contained in these baths are applied to the surfaces of the cellophane during its passage through the baths and then dried onto such surfaces when the cellophane is subsequently passed through the drier portion of the machine. Such bath treatments of the cellulose hydrate films in general cause an increased tendency for blocking. If, for example, an improved anchoring action is sought after, optimal surface sliding characteristics are precluded and the undesired blocking effect occurs when the treated film is rolled and later unrolled for further processing.

As a consequence, endeavors have been made to eliminate such blocking as much as possible without at the same time having to give up the various other desired properties produced by other additives to the treating baths.

So-called antiblocking agents have already been developed for simple softening baths which contain no additions of cationically active lubricants or anchoring agents. For example, in a known process finely divided metal or metalloid oxides having a particle size of less than 0.15, which, for example, can be made in a known manner, for instance, by the thermal decomposition of volatile metal or metalloid compounds, especially halides, in the gas phase in the presence of agents having a hydrolysing action to form aerosols which are recovered as aerogels. A preferred aerogel of this type is the finely disperse pyrogenic silica which is produced by the thermal gas phase decomposition of volatile silicon compounds such as silicon tetrachloride in a flame produced by the combustion of hydrogen containing gases. Other suitable oxide aerogels, for example, are those of titanium, zirconium, zinc or aluminum produced in an analogous manner. The oxide aerogels need not be employed in pure state as mixtures of such oxides or mixed oxides can also be used. These highly disperse colloids expediently are converted into their aqueous dispersons which are then incorporated in the softeners or softener solutions. Care must be taken to ensure a good distribution of these dispersions as the stability of the baths as well as the effect obtained depends to a great extent thereon.

However, when attempts are made to employ silica dispersions in softening baths containing lubricants and/or anchoring agents, the presence of cationically active film processing agents such as the lubricants and anchoring agents cause coagulation of the dispersions. As such cationically active film processing agents are being used in an ever increasing extent in the processing of cellulose hydrate films and furthermore as experience shows when such lubricants or anchoring agents are used the use of additional antiblocking agents cannot be dispensed with, the use of silicic acid suspensions in softening baths is considerably curtailed because of the coagulation of the electronegatively charged silicic acid particles. On the other hand, in the absence of antiblocking agents the surface characteristics necessary for subsequent processing are not provided.

For this reason a proposal has already been made in the field of textile processing wherein similar problems occur to treat natural cellulose or regenerated cellulose in fiber, yarn or woven fabric form for the purpose of reducing fiber slippage with suspensions which contain 0.7 to 1.4 parts by weight of a finely divided hydroxyl group containing inorganic filler such as silicic acid and 25 parts by Weight of a 50% aqueous polyethylene imine paste per 1000 parts by weight of suspension. Such aqueous treating suspensions are obtained by stirring 25 parts by weight of a 50% aqueous polyethylene imine paste into 200 parts by weight of water at 20 C. with subsequent addition of a further quantity of water to provide a highly fluid solution and thereafter adding 5 to 10 parts by Weight of a 14% dispersion of finely divided silicic acid, also thinned out with water, while stirring at 20 C. and then supply; ing suificient water to the resulting suspension to provide a total 1000 parts by Weight thereof.

Experience has shown that when the above described method is employed for the production of the silicic acid polyethylene imine suspensions, it is not possible to increase the quantity of the silicic acid incorporated as upon addition, as a maximum, of 2025 parts by weight of a 14% silicic acid dispersion, that is, 2.8-3.5 parts by weight of silicic acid, coagulation already occurs. Consequently, with such known method it is only possible to produce silicic acid polyethylene imine suspensions which per 1000 parts by Weight contain 12.5 parts by weight of polyethylene imine and as a maximum 2.8 to 3.5 parts by weight of silicic acid. While such suspensions are sufiicient for the treatment of textile fibers and textile products produced therefrom, they are not suited for alleviating the diificulties which occur in different types of surface processing of cellulose hydrate films.

It therefore is an object of the invention to provide a process for the processing of cellulose hydrate films for improvement of their surface characteristics in which such films pass through a bath which in addition to softeners contains added cationically active lubricants and/or anchoring agents and sufiiciently high content of dispersed oxide aerogels as antiblocking agents so that such good surface characteristics are provided in the treated cellulose hydrate films that they can be stored in stacked or rolled up form without danger of blocking prior to subsequent processing such as lacquering, coating, cutting, printing and the like.

According to the invention it was found that this could be achieved by adding to the bath the modified products obtained from finely divided oxide aerogels having a particle size of less than about 0.15;/. and known anchoring agents, for example, high molecular weight organic compounds in hydrophilic form, especially polyethylene imines or precondensation products of urea, thiourea and/ or melamine with formaldehyde, which are obtained by intensive dispersion of the finely divided oxide aerogels in dry form in an aqueous solution of the high molecular weight organic compound.

By working in the dry finely divided oxide aerogels into an aqueous solution of a cationically active anchoring agent such as polyethylene imine which, for example, can be obtained in a known manner by catalytic acid (cationic) polymerization of ethylene imine, rather than working in the oxide aerogels in the form of an aqueous dispersion containing, for example, a small quantity of dispersed silicic acid, it is possible to disperse surprisingly large quatities of the finely divided oxide aerogels so that, for example, stable, non-coagulating dispersions can be obtained which contain between 80 and 200 parts, preferably, between 120 and 150 parts, by weight of silicic acid and -40 parts, preferably 15-20 parts by weight of polyethylene imine per 1000 parts by weight of the dispersion.

The stable dispersions produced according to the invention can either be used together with the above mentioned anchoring and/or lubricating agents or these products can be added to a bath preceding the usual softener bath.

The production and use of the dispersions according to I the invention are illustrated in the following example.

Example 83.5 liters of distilled water were placed in a stirring vessel and 4 kg. of an aqueous 50% polyethylene imine paste dissolved therein. Then 12.5 kg. of a pyrogenic silica aerogel product having a primary particle size of about l040 m and a surface of 6080 m /g. were stirred in in dry form and then intensively dispersed therein with a high capacity stirrer.

An excellent non-coagulating dispersion was obtained.

Such dispersion was added to an aqueous softener bath which in addition to 4% of glycerine also contained 0.5 g. per liter of a water soluble urea formaldehyde precondensate as an anchoring agent. The quantity of such dispersion incorporated in the softener bath was 5.0 cc. per liter. A regenerated cellulose film was passed through such bath at 25 C. and then freed of excess liquid by being passed through rubber squeezing rollers and dried on rollers heated to -90 C. The resulting treated film had good surface characteristics and could be rolled up and stored for longer periods of time without danger of blocking.

Similar good results were obtained when the silica aerogel used above was replaced by a mixed oxide aerogel containing about 98.3% of SiO and about 03-13% of A1 0 and the remainder other oxides which may be disregarded and having about the same particle size and surface area as such silica aerogei.

The polyethylene imine employed was one obtained by catalytic acid polymerization of ethylene imine which was terminated by neutralization just before complete water solubility was lost. The 50% aqueous solution was of alkaline reaction. Such water soluble polyethylene imine product has already achieved wide use in the paper industry to increase the wet strength of paper and is, for example, available as the well-known product Polymin-P.

I claim:

1. In a method of improving the surface characteristics of cellulose hydrate films in which such films are passed through an aqueous bath containing a cationically active film processing agent, the step of incorporating in such bath as an anti-blocking agent an effective amount of a stable aqueous suspension of pyrogenic silica aerogel having a particle size of less than 0.15 obtained by intensively dispersing the silica aerogel in dry form in an aqueous solution of polyethylene imine in such proportions that the aqueous suspension contains 8 to 20% by weight of silica aerogel and 1.5 to 4% by weight of polyethylene imine, said bath also containing a softening agent for said cellulose hydrate film.

2. An antiblocking agent for use in baths employed for the processing of cellulose hydrate films consisting essentially of a stable aqueous dispersion containing 8 to 20% by weight of dispersed pyrogenic silica having a particle size of less than 0.15 2 and 1.5 to 4% by weight of polyethylene imine dissolved in the aqueous phase of such dispersion.

3. An antiblocking agent for use in baths employed for the processing of cellulose hydrate films comprising a stable aqueous dispersion containing 12 to 15% by weight of dispersed pyrogcnic silica having a particle size of less than 0.15 and 1.5 to 2.0% by weight of polyethylene imine dissolved in the aqueous phase of such dispersion.

4. A method of producing a stable aqueous dispersion containing 8 to 20% by weight of a pyrogenic silica having a particle size of less than 0.15 1. which comprises intensively dispersing a pyrogenic silica aerogel having a particle size of less than 0.15 1. in dry form in an aqueous solution of polyethylene imine in such proportions that the aqueous suspension contains 8 to 20% by weight of the silica aerogel and 1.5 to 4.0% by weight of polyethylene imine.

References Qited UNITED STATES PATENTS 3,013,901 4/1961 Bugosh 117-144X 2,892,730 6/1959 Kloepfer et a1. l06263 X FOREIGN PATENTS 1,081,410 5/1960 Germany.

713,211 8/1954 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

J. B. EVANS, Assistant Examiner. 

1. IN A METHOD OF IMPROVING THE SURFACE CHARACTERISTICS OF CELLULOSE HYDRATE FILMS IN WHICH SUCH FILMS ARE PASSED THROUGH AN AQUEOUS BATH CONTAINING A CATIONICALLY ACTIVE FILM PROCESSING AGENT, THE STEP OF INCORPORATING IN SUCH BATH AS AN ANTI-BLOCKING AGENT AN EFFECTIVE AMOUNT OF A STABLE AQUEOUS SUSPENSION OF PYROGENIC SILICA AEROGEL HAVING A PARTICLE SIZE OF LESS THAN THAN 0.15U OBTAINED BY INTENSIVELY DISPERSING THE SILICA AEROGEL IN DRY FORM IN AN AQUEOUS SOLUTION OF POLYETHYLENE IMINE IN SUCH PROPORTIONS THAT THE AQUEOUS SUSPENSION CONTAINS 8 TO 20A% BY WEIGHT OF SILICA AEROGEL AND 1.5 TO 4% BY WEIGHT OF POLYETHYLENE IMINE, SAID BATH ALSO CONTAINING A SOFENTING AGENT FOR SAID CELLULOSE HYDRATE FILM.
 2. AN ANTIBLOCKING AGENT FOR USE IN BATHS EMPLOYED FOR THE PROCESSING OF CELLULOSE HYDRATE FILMS CONSISTING ESSENTIALLY OF A STABLE AQUEOUS DISPERSION CONTAINING 8 TO 20% BY WEIGHT OF DISPERSED PYROGENIC SILICA HAVING A PARTICLE SIZE OF LESS THAN 0.15U AND 1.5 TO 4% BY WEIGHT OF POLYETHYLENE IMINE DISSOLVED IN THE AQUEOUS PHASE OF SUCH DISPERSION. 